Computer simulations of physiologically based pharmacokinetic models are used to study the uptake, metabolism, and elimination of compounds administered by inhalation. The application of these models to specific experimental data sets requires compound and animal specific constants. Systems have been developed to obtain values for these constants. Tissue partition constants are determined by vial equilibration. Metabolic rate constants are taken from published values from in vitro measurements or estimated from measurements of uptake kinetics in a closed exposure system. Literature values are scaled to provide values for physiological constants. Equipment and procedures have been developed to measure respiratory minute volume during inhalation exposures. Methods have been developed to acquire measurements of the exposure compound and major metabolites in blood and major tissues at various time points during and after treatment via inhalation. These data are used in the evaluation of the models.